We’ve compared a draft of the synthesis report with
that published in 2007 to find out how they compare. Here are the
key areas of change.

Irreversible impacts are being felt
already

The AR5 draft synthesis begins with a decisive
statement that human influence on the climate is “clear”, that
recent emissions are the highest in history and that “widespread
and consequential impacts” are already being felt.

This opening line shows how much has changed in
the way the authors present their findings. In contrast, the 2007
report opened with a discussion of scientific progress and an
extended paragraph on definitions.

There are also a couple of clear thematic
changes in the 2014 draft. The first, repeated frequently
throughout, is the idea that climate change impacts are already
being felt.

For instance it says that the height of coastal
floods has already increased and that climate-change-related risks
from weather extremes such as heatwaves and heavy rain are “already
moderate”.

These observations are crystallised in a long
section on Article 2 of the UN’s climate change convention, which
has been signed by every country of the world. Article 2 says that
the objective of the convention is to avoid dangerous climate
change.

The AR5 draft implies the world may already have
failed in this task:

“Depending on value
judgements and specific circumstances, currently observed impacts
might already be considered dangerous for some
communities.”

The second theme is a stronger emphasis on
irreversible impacts compared to the 2007 version. The 2014 draft
says:

“Continued emission of
greenhouse gases will cause further warming and long-lasting
changes in all components of the climate system, increasing the
likelihood of severe, pervasive and irreversible impacts for people
and ecosystems.”

It says that a large fraction of warming will be
irreversible for hundreds to thousands of years and that the
Greenland ice sheet will be lost when warming reaches between one
and four degrees above pre-industrial temperatures. Current warming
since pre-industrial times is about 0.8 degrees celsius.

In effect the report has switched tense from
future conditional (“could experience”) to present continuous (“are
experiencing”). For instance it says there are signs that
some corals and Arctic ecosystems “are already experiencing
irreversible regime shifts” because of warming.

Stronger evidence than before

As well as these thematic changes in the use of
language, the AR5 synthesis comes to stronger conclusions in many
other areas.

This is largely because the scientific evidence
has solidified in the intervening seven years, the IPCC
says.

We’ve drawn together a collection of
side-by-side statements so you can see for yourself how the
conclusions have changed. Some of the shifts in language are subtle
– but they are significant all the same.

The authors of the latest synthesis report seem
to have made an effort to boost the impact of their words. They’ve
used clearer and more direct language along with what appears to be
a stronger emphasis on the negative consequences of
inaction.

The language around relying on adaptation to
climate change has also shifted. It now more clearly emphasises the
need for mitigation to cut emissions, if the worst impacts of
warming are to be avoided.

Some are bound to read this as an unwelcome
excursion into advocacy. But others will insist it is simply a case
of better presenting the evidence that was already there, along
with advances in scientific knowledge.

Government representatives have the chance to go
over the draft AR5 synthesis report with a fine toothcomb when they
meet during 27-31 October.